This invention relates generally to a sprocket wheel having sprocket teeth each in the form of divided tooth sections with pockets between the teeth for the reception of horizontal links of a drive chain engaging cupped outer tips at the flanks or sides of the sections, and more particularly to such a sprocket wheel wherein the cupped tips of each pair of tooth sections slope in the running direction of the chain.
Chain link drive sprockets, of the type which the invention pertains, are known to have double curved surfaces at the cupped outer tips at the flanks against which the horizontal chain links of the drive chain bear. The curvature of these surfaces is such that the chain links are cupped at the flanks of the teeth for driving the chain by the sprocket. Thus, the double curved surfaces provide contact surfaces for the chain links in such a manner that the chain links contact the surfaces throughout a wide area which thereby contributes to an unfavorable distribution of the forces needed to effectively drive the chain. Trouble-free operation between the chain links and the tooth flanks therefore becomes difficult to achieve with the aforedescribed prior art design. For example, the degree of effectiveness of the entire design is so unfavorable that, when measuring the results achieved, only 55 to 75% of the sprocket drive performance will reach the link chain. The unfavorable interplay between the chain and the tooth flanks may be due to the fact that the shape of the round steel chain links especially in the area of the arcs thereof, fluctuates and is so variable in the distribution because of the different factors of influence of the type of material used and the type of manufacture, that an optimum contact surface between the rounded portions of the horizontal chain links and the tooth flanks cannot be achieved. Thus, the horizontal chain links effect a particularly high concentrated pressure (Hertz' pressure) against the sprocket teeth so that the chain links are not snuggly received and cupped by the tooth sections. This leads to the development of premature and dangerous wear in the form of so-called "duck tails" which considerably decrease the fatigue strength of the chain and may thus cause downtime in the operation of the drive with accompanying increased expenses in labor and equipment.
Moreover, the unfavorable interplay between the chain and the sprocket wheel is due to the fact that the spacing tolerances of the sprocket wheel and of the chain generally are only responsible for the transfer of forces.
German Utility Patent No. 16 81 958 discloses another known drive sprocket wheel in which the cupped outer tips at the flanks of the tooth sections each have a radius of curvature designed to be equal to the radius of the chain links bearing thereagainst. In such an arrangement, an optimum contact surface between the rounded portions of the horizontal chain links and the curved tips are likewise incapable of being achieved so that the previously described particularly high pressures occur.
Other approaches taken in dealing with the problems described above include a shortening of the chain so that it may be stretched to the desired length during the driving operation. In so doing, however, deviations from the circular arc of the chain links develop whereupon undesirable so-called "pointed arches" develop.
The snug reception of the horizontal chain links by the sprocket teeth is not the only important design parameter for the drive sprocket. The location of the contact point between the chain links and the tooth flanks surfaces is likewise quite important.
And, it is not only important as to how the chain links contact the tooth flanks surfaces, but the location of such contact and the number of chain links which participate in the transfer of forces to the sprocket wheel are likewise important factors.